63 research outputs found
Cosmological imprints of string axions in plateau
We initiate a study on various cosmological imprints of string axions whose
scalar potentials have plateau regions. In such cases, we show that a delayed
onset of oscillation generically leads to a parametric resonance instability.
In particular, for ultralight axions, the parametric resonance can enhance the
power spectrum slightly below the Jeans scale, alleviating the tension with the
Lyman forest observations. We also argue that a long-lasting resonance
can lead to an emission of gravitational waves at the frequency bands which are
detectable by gravitational wave interferometers and pulsar timing arrays.Comment: 5 pages, 5 figures; v2: references added, v3: matches with the
published versio
Conservation of with radiative corrections from heavy field
In this paper, we address a possible impact of radiative corrections from a
heavy scalar field on the curvature perturbation . Integrating
out , we derive the effective action for , which includes the loop
corrections of the heavy field . When the mass of is much larger
than the Hubble scale , the loop corrections of only yield a local
contribution to the effective action and hence the effective action simply
gives an action for in a single field model, where, as is widely known,
is conserved in time after the Hubble crossing time. Meanwhile, when
the mass of is comparable to , the loop corrections of can
give a non-local contribution to the effective action. Because of the non-local
contribution from , in general, may not be conserved, even if the
classical background trajectory is determined only by the evolution of the
inflaton. In this paper, we derive the condition that is conserved in
time in the presence of the radiative corrections from . Namely, we show
that when the scaling symmetry, which is a part of the diffeomorphism
invariance, is preserved at the quantum level, the loop corrections of the
massive field do not disturb the constant evolution of at super
Hubble scales. In this discussion, we show the Ward-Takahashi identity for the
scaling symmetry, which yields a consistency relation for the correlation
functions of the massive field .Comment: 27 pages, 1 figure; v2: updated references and minor revision
Strong restriction on inflationary vacua from the local gauge invariance I: Local gauge invariance and infrared regularity
The primordial perturbation is widely accepted to be generated through the
vacuum fluctuation of the scalar field which drives inflation. It is, however,
not completely clear what is the natural vacuum in the inflationary universe
particularly in the presence of non-linear interactions. In this series of
papers, we will address this issue, focusing on the condition required for the
removal of the divergence from the infrared (IR) contribution to loop diagrams.
We show that requesting the gauge invariance in the local observable universe
guarantees the IR regularity of the loop corrections beginning with a simple
initial state. In our previous works, the IR regularity condition was discussed
using the slow roll expansion, which restricts the background evolution of the
inflationary universe. We will show more generally that requesting the gauge
invariance/the IR regularity leads to non-trivial constraints on the allowed
quantum states.Comment: 14 page
Strong restriction on inflationary vacua from the local gauge invariance III: Infrared regularity of graviton loops
It has been claimed that the super Hubble modes of the graviton generated
during inflation can make loop corrections diverge. Even if we introduce an
infrared (IR) cutoff at a comoving scale as an ad hoc but a practical way for
the regularization, we encounter the secular growth, which may lead to the
breakdown of perturbative expansion for a sufficiently long lasting inflation.
In this paper, we show that the IR pathology concerning the graviton can be
attributed to the presence of residual gauge degrees of freedom in the local
observable universe as in the case of the adiabatic curvature perturbation. We
will show that choosing the Euclidean vacuum as the initial state ensures the
invariance under the above-mentioned residual gauge transformations. We will
also show that as long as we consider a gauge invariant quantity in the local
universe, we encounter neither the IR divergence nor the secular growth. The
argument in this paper applies to general single field models of inflation up
to a sufficiently high order in perturbation.Comment: 34 pages; v2: minor revision, published in PTEP. arXiv admin note:
text overlap with arXiv:1306.446
Holographic inflation and the conservation of
In a holographic description of inflation, cosmological time evolution in the
bulk is expected to correspond to the renomalization group (RG) flow in a dual
boundary theory. Here, we analyze this expectation by computing the correlation
functions of the curvature perturbation holographically. For this
purpose, we use a deformed conformal field theory at the boundary, with a
single deformation operator. In standard single field models of inflation,
is known to be conserved at large scales under very general conditions.
However, we find that this is not generically the case in the dual description.
The requirement that higher correlators of should be conserved severely
restricts the possibilities for the RG flow. With such restriction, the power
spectrum must follow an exact power law, at least within the regime
of validity of conformal perturbation theory.Comment: 27 pages, 1 figure; v2: version to appear in JHE
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